System:

Ubuntu: 18.04 LTS

Passenger: 5.3.1

nginx with libnginx-mod-http-passenger

$ sudo nginx -t

Returns:

PassengerLoggingAgent: /usr/lib/x86_64-linux-gnu/libcurl.so.4: version `CURL_OPENSSL_3' not found (required by PassengerLoggingAgent)
2018/06/04 02:28:40 [alert] 10411#0: Unable to start the Phusion Passenger watchdog because it encountered the following error during startup: Unable to start the Phusion Passenger logging agent: it seems to have crashed during startup for an unknown reason, with exit code 1 (-1: Unknown error)